The present invention relates to the field of data recording and playback and, more particularly, to improvements in apparatus for controlling the radial position of a write/read head relative to a data storage disk so that information can be written on (or read from) a desired data track.
Heretofore, a variety of radial access mechanisms have been proposed and utilized for controlling the radial position of a write/read head relative to the recording surface of a data storage disk (e.g. optical, magneto-optic and magnetic disks). Typically, such mechanisms function to advance the head along a straight or arcuate trajectory in a plane parallel to the plane of disk rotation. In providing a linear head trajectory, many different voice-coil linear actuators designs have been used.
In U.S. Pat. No. 4,763,314 issued to McCaslin et al, there is disclosed a moving coil linear actuator for controlling the radial position of a write/read head in an optical disk recording apparatus. The actuator comprises a carriage having six roller bearings which are positioned to engage and be guided by a pair of spaced, parallel rods rigidly mounted on a support plate. The roller bearings and rods cooperate to provide an "exact constraint" whereby the motion of the carriage is constrained to a rectilinear path. Though not expressly disclosed, it appears that the bearings themselves are preloaded within the carriage so as to exert equal forces on the support rods. While it is possible to preload each bearing in a relatively large access mechanism, such a preloading scheme is increasingly problematic as the size of the mechanism is miniaturized. Also in this actuator design, the carriage is driven by two discrete linear motors, each comprising its own separate moving coil. The need for two coils can complicate the task of exerting a uniform force on the carriage in a direction parallel to the intended direction of travel.